#include "stack.h"
#include <string.h>

int
stack_grow(struct stack *st, size_t new_size)
{
    void **new_st;

    if (st->asize >= new_size)
        return 0;

    new_st = realloc(st->item, new_size * sizeof(void *));
    if (new_st == NULL)
        return -1;

    memset(new_st + st->asize, 0x0,
        (new_size - st->asize) * sizeof(void *));

    st->item = new_st;
    st->asize = new_size;

    if (st->size > new_size)
        st->size = new_size;

    return 0;
}

void
stack_free(struct stack *st)
{
    if (!st)
        return;

    free(st->item);

    st->item = NULL;
    st->size = 0;
    st->asize = 0;
}

int
stack_init(struct stack *st, size_t initial_size)
{
    st->item = NULL;
    st->size = 0;
    st->asize = 0;

    if (!initial_size)
        initial_size = 8;

    return stack_grow(st, initial_size);
}

void *
stack_pop(struct stack *st)
{
    if (!st->size)
        return NULL;

    return st->item[--st->size];
}

int
stack_push(struct stack *st, void *item)
{
    if (stack_grow(st, st->size * 2) < 0)
        return -1;

    st->item[st->size++] = item;
    return 0;
}

void *
stack_top(struct stack *st)
{
    if (!st->size)
        return NULL;

    return st->item[st->size - 1];
}

